1. Field
Embodiments of the present disclosure generally relate to the fabrication of integrated circuits and particularly to a method for creating reduced critical dimensions in a feature formed in a hardmask used for pattern transfer.
2. Description of the Related Art
Reducing the size of integrated circuits (ICs) results in improved performance, increased capacity, and/or reduced cost. Each size reduction requires more sophisticated techniques to form the ICs. Photolithography is commonly used to pattern ICs on a substrate. An exemplary feature of an IC is a line of a material which may be a metal, semiconductor, or insulator. Line width is the width of the line and the spacing is the distance between adjacent lines. Pitch is defined as the distance between a same point on two adjacent lines. The pitch is equal to the sum of the line width and the spacing. However, due to factors such as optics and light or radiation wavelength, photolithography techniques have a minimum pitch below which a particular photolithographic technique may not reliably form features. Thus, the minimum pitch of a photolithographic technique can limit feature size reduction. Similarly, patterning tools designed to create vias or line interconnects 100 nm or wider are not commonly able to create smaller vias. Therefore, as devices shrink to these small dimensions, current lithography processes are challenged to create patterns with the required critical dimensions (CD). To avoid having to redesign the current lithography tools, new methods are needed to shrink the critical dimension of IC lines and via interconnects etched into a substrate.
Currently, conformal layers used to shrink critical dimensions, such as a reduced dimension pattern in a hardmask, are formed by atomic layer deposition (ALD) using an etchable material such as silicon oxide. However, the deposited material quality can be difficult to control, resulting in low density, poor mechanical strength, and degraded chemical resistance to subsequent etching chemistries. High stresses in ALD oxides can also lead to buckling and deformation of under-layers, as well as delamination due to poor adhesion and mismatches in chemical compatibility. Additionally, oxide materials require a wet clean process for removal after etching. Wet clean is an isotropic process which typically leads to CD loss and under-cut issues.
Plasma enhanced chemical vapor deposition (PECVD) of carbon films is an alternative for forming a reduced dimension pattern in a hardmask material due to the formed carbon layer's etch selectivity and easy removal using conventional dry ashing plasma processes. Generally, deposition of carbon films for producing reduced dimension patterns in a hardmask is practiced at temperatures exceeding 120° C. to achieve acceptable step coverage, conformality with minimum pattern loading effect, gap filling, and planarization on high aspect ratio structures. These conventional carbon deposition processes have limited use due to the high temperatures that are required to form these types of layers. The high temperature PECVD deposition of conformal carbon thus prevents its disposition onto soft carbonaceous materials such as photoresists that have a decomposition temperature typically less than 120° C.
Given the current state of the art, there is a need for a low temperature method for the formation of carbon containing film directly upon a patterned photoresist layer, followed by removal by a dry ashing process.